1. Field of the Invention
The present invention relates to a pickup device used for a dielectric recording/reproducing apparatus for recording/reproducing information with high density in/from microdomains in a dielectric substance.
2. Description of the Related Art
As high-density, large-capacity recording/reproducing apparatuses of randomly accessible type, there are known an optical disk apparatus and a hard disc drive (HDD) apparatus. Moreover, a recording/reproducing technique using a scanning nonlinear dielectric microscopy (SNDM) for the nanoscale analysis of a dielectric (ferroelectric) material has been recently proposed by the inventors of the present invention.
In optical recording, which uses an optical pickup with a laser as a light source, data is recorded by forming pits that are concavo-convex on a disk surface or by forming the crystal phase of a phase shift medium, and the data is reproduced by using the difference in the reflectance of amorphous phases or using the magneto optical effect. However, the pickup is large, which is not appropriate for high-speed reading, and the size of the recording pit is defined by the diffraction limit of light, so that its recording density is limited to 50 G bit/inch2.
In the longitudinal recording of magnetic recording as represented by the HDD, a magnetic resistance (MR) head has been recently realized using giant magnetic resistance (GMR) and its recording density is expected to be larger than that of the optical disk by using perpendicular magnetic recording. However, the recording density is limited to 1 T bit/inch2 due to thermal fluctuation of magnetic recording information and the presence of a Bloch wall in a portion in which a code or sign is reversed or changed, even if patterned media are used considering the above cause.
Using the SNDM to measure a nonlinear dielectric constant of a ferroelectric material, it is possible to detect the plus and minus of a ferroelectric domain. Moreover, the SNDM is found to have sub-nanometer resolution using an electrically conductive cantilever (or probe) which is used for an atomic force microscopy (AFM) or the like and which is provided with a small probe on its tip portion. In the SNDM, a resonance circuit is formed with the probe, an inductor and an oscillator connected with the probe, a capacitance of the dielectric (ferroelectric) material just under the probe, and a return electrode, which is placed near the tip portion of the probe, for returning an alternating electric field from the tip portion of the probe through the dielectric (ferroelectric) material. As described above, the conventional SNDM is designed to be an analysis apparatus in which the return electrode used is a metal conductor of a ring shape of 7 mm outer diameter, 3 mm inner diameter, and about 0.5 mm thickness, placed so as to surround the tip portion of the probe.
However, the above-described SNDM has not been specially developed in view of a recording/reproducing apparatus and thus have such a problem that the probe is large or that assembling is complicated. Moreover, if it has a plurality of probes in order to increase a data transfer rate, the complication increases more.